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><H1
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><A
NAME="CATALOG-PG-STATISTIC"
>45.40. <TT
CLASS="STRUCTNAME"
>pg_statistic</TT
></A
></H1
><P
>   The catalog <TT
CLASS="STRUCTNAME"
>pg_statistic</TT
> stores
   statistical data about the contents of the database.  Entries are
   created by <A
HREF="sql-analyze.html"
>ANALYZE</A
>
   and subsequently used by the query planner.  Note that all the
   statistical data is inherently approximate, even assuming that it
   is up-to-date.
  </P
><P
>   Normally there is one entry, with <TT
CLASS="STRUCTFIELD"
>stainherit</TT
> =
   <TT
CLASS="LITERAL"
>false</TT
>, for each table column that has been analyzed.
   If the table has inheritance children, a second entry with
   <TT
CLASS="STRUCTFIELD"
>stainherit</TT
> = <TT
CLASS="LITERAL"
>true</TT
> is also created.  This row
   represents the column's statistics over the inheritance tree, i.e.,
   statistics for the data you'd see with
   <TT
CLASS="LITERAL"
>SELECT <TT
CLASS="REPLACEABLE"
><I
>column</I
></TT
> FROM <TT
CLASS="REPLACEABLE"
><I
>table</I
></TT
>*</TT
>,
   whereas the <TT
CLASS="STRUCTFIELD"
>stainherit</TT
> = <TT
CLASS="LITERAL"
>false</TT
> row represents
   the results of
   <TT
CLASS="LITERAL"
>SELECT <TT
CLASS="REPLACEABLE"
><I
>column</I
></TT
> FROM ONLY <TT
CLASS="REPLACEABLE"
><I
>table</I
></TT
></TT
>.
  </P
><P
>   <TT
CLASS="STRUCTNAME"
>pg_statistic</TT
> also stores statistical data about
   the values of index expressions.  These are described as if they were
   actual data columns; in particular, <TT
CLASS="STRUCTFIELD"
>starelid</TT
>
   references the index.  No entry is made for an ordinary non-expression
   index column, however, since it would be redundant with the entry
   for the underlying table column.  Currently, entries for index expressions
   always have <TT
CLASS="STRUCTFIELD"
>stainherit</TT
> = <TT
CLASS="LITERAL"
>false</TT
>.
  </P
><P
>   Since different kinds of statistics might be appropriate for different
   kinds of data, <TT
CLASS="STRUCTNAME"
>pg_statistic</TT
> is designed not
   to assume very much about what sort of statistics it stores.  Only
   extremely general statistics (such as nullness) are given dedicated
   columns in <TT
CLASS="STRUCTNAME"
>pg_statistic</TT
>.  Everything else
   is stored in <SPAN
CLASS="QUOTE"
>"slots"</SPAN
>, which are groups of associated columns
   whose content is identified by a code number in one of the slot's columns.
   For more information see
   <TT
CLASS="FILENAME"
>src/include/catalog/pg_statistic.h</TT
>.
  </P
><P
>   <TT
CLASS="STRUCTNAME"
>pg_statistic</TT
> should not be readable by the
   public, since even statistical information about a table's contents
   might be considered sensitive.  (Example: minimum and maximum values
   of a salary column might be quite interesting.)
   <A
HREF="view-pg-stats.html"
><TT
CLASS="STRUCTNAME"
>pg_stats</TT
></A
>
   is a publicly readable view on
   <TT
CLASS="STRUCTNAME"
>pg_statistic</TT
> that only exposes information
   about those tables that are readable by the current user.
  </P
><DIV
CLASS="TABLE"
><A
NAME="AEN88374"
></A
><P
><B
>Table 45-40. <TT
CLASS="STRUCTNAME"
>pg_statistic</TT
> Columns</B
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><COL><COL><COL><COL><THEAD
><TR
><TH
>Name</TH
><TH
>Type</TH
><TH
>References</TH
><TH
>Description</TH
></TR
></THEAD
><TBODY
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>starelid</TT
></TD
><TD
><TT
CLASS="TYPE"
>oid</TT
></TD
><TD
><TT
CLASS="LITERAL"
><A
HREF="catalog-pg-class.html"
><TT
CLASS="STRUCTNAME"
>pg_class</TT
></A
>.oid</TT
></TD
><TD
>The table or index that the described column belongs to</TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>staattnum</TT
></TD
><TD
><TT
CLASS="TYPE"
>int2</TT
></TD
><TD
><TT
CLASS="LITERAL"
><A
HREF="catalog-pg-attribute.html"
><TT
CLASS="STRUCTNAME"
>pg_attribute</TT
></A
>.attnum</TT
></TD
><TD
>The number of the described column</TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>stainherit</TT
></TD
><TD
><TT
CLASS="TYPE"
>bool</TT
></TD
><TD
>&nbsp;</TD
><TD
>If true, the stats include inheritance child columns, not just the
       values in the specified relation</TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>stanullfrac</TT
></TD
><TD
><TT
CLASS="TYPE"
>float4</TT
></TD
><TD
>&nbsp;</TD
><TD
>The fraction of the column's entries that are null</TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>stawidth</TT
></TD
><TD
><TT
CLASS="TYPE"
>int4</TT
></TD
><TD
>&nbsp;</TD
><TD
>The average stored width, in bytes, of nonnull entries</TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>stadistinct</TT
></TD
><TD
><TT
CLASS="TYPE"
>float4</TT
></TD
><TD
>&nbsp;</TD
><TD
>The number of distinct nonnull data values in the column.
      A value greater than zero is the actual number of distinct values.
      A value less than zero is the negative of a multiplier for the number
      of rows in the table; for example, a column in which values appear about
      twice on the average could be represented by
      <TT
CLASS="STRUCTFIELD"
>stadistinct</TT
> = -0.5.
      A zero value means the number of distinct values is unknown.
      </TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>stakind<TT
CLASS="REPLACEABLE"
><I
>N</I
></TT
></TT
></TD
><TD
><TT
CLASS="TYPE"
>int2</TT
></TD
><TD
>&nbsp;</TD
><TD
>       A code number indicating the kind of statistics stored in the
       <TT
CLASS="REPLACEABLE"
><I
>N</I
></TT
>th <SPAN
CLASS="QUOTE"
>"slot"</SPAN
> of the
       <TT
CLASS="STRUCTNAME"
>pg_statistic</TT
> row.
      </TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>staop<TT
CLASS="REPLACEABLE"
><I
>N</I
></TT
></TT
></TD
><TD
><TT
CLASS="TYPE"
>oid</TT
></TD
><TD
><TT
CLASS="LITERAL"
><A
HREF="catalog-pg-operator.html"
><TT
CLASS="STRUCTNAME"
>pg_operator</TT
></A
>.oid</TT
></TD
><TD
>       An operator used to derive the statistics stored in the
       <TT
CLASS="REPLACEABLE"
><I
>N</I
></TT
>th <SPAN
CLASS="QUOTE"
>"slot"</SPAN
>.  For example, a
       histogram slot would show the <TT
CLASS="LITERAL"
>&lt;</TT
> operator
       that defines the sort order of the data.
      </TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>stanumbers<TT
CLASS="REPLACEABLE"
><I
>N</I
></TT
></TT
></TD
><TD
><TT
CLASS="TYPE"
>float4[]</TT
></TD
><TD
>&nbsp;</TD
><TD
>       Numerical statistics of the appropriate kind for the
       <TT
CLASS="REPLACEABLE"
><I
>N</I
></TT
>th <SPAN
CLASS="QUOTE"
>"slot"</SPAN
>, or null if the slot
       kind does not involve numerical values
      </TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>stavalues<TT
CLASS="REPLACEABLE"
><I
>N</I
></TT
></TT
></TD
><TD
><TT
CLASS="TYPE"
>anyarray</TT
></TD
><TD
>&nbsp;</TD
><TD
>       Column data values of the appropriate kind for the
       <TT
CLASS="REPLACEABLE"
><I
>N</I
></TT
>th <SPAN
CLASS="QUOTE"
>"slot"</SPAN
>, or null if the slot
       kind does not store any data values.  Each array's element
       values are actually of the specific column's data type, so there
       is no way to define these columns' type more specifically than
       <TT
CLASS="TYPE"
>anyarray</TT
>.
      </TD
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